Such a boring bar as well as such a method are for example described in WO 2014/195007 A1.
Bearing shafts such as camshafts or crankshafts in motor vehicles are normally supported in bearing holes, hereinafter termed holes for short, on a plurality of bearing supports that are axially separated from each other. At the same time, the individual holes are normally bored to a final dimension with the assistance of a so-called line boring bar. This has blades that are offset from each other in an axial direction by the spacing distance and are each provided for machining a corresponding hole so that a plurality of holes can be machined simultaneously by means of such a line boring bar by the blades separated from each other in an axial direction.
Working positions that each have a blade are therefore disposed on the boring bar at locations corresponding to the distance between the holes. Normally, only one blade is present for each working position.
For the boring process, the boring bar must be guided or supported. Directly supporting the boring bar by means of guide elements in the region of the corresponding blades, as is known for example with reamers, is not readily feasible in this regard since the boring bar must first be inserted through the rough, yet-to-be machined holes.
Consequently a solution for supporting the boring bar is described in WO 2014/195007 which originates from the applicant, i.e., in particular an alternatively-designed boring bar by means of which efficient machining of holes that are aligned with each other is enabled. For this purpose, the boring bar has a main body with an axis of rotation and a plurality of cutting elements separated from each other in an axial direction, as well as in addition at least one guide element for guiding the main body within a guide hole, wherein the guide elements are separated from the axis of rotation by a guide radius. The main body is furthermore divided into a functional region and an eccentric region, wherein the cutting elements as well as the guide elements are distributed about the main body over an angular range of less than 180°. In addition, the circumferential face of the main body in the eccentric region is at a distance from the axis of rotation that is less in comparison with the guide radius so that the main body can be guided eccentrically through a corresponding hole with an unmachined rough radius that is less than the guide radius.
According to a preferred development, the arrangement of a balance element is additionally provided, wherein the balance element forms a component of the main body that accordingly can be divided into a basic body and the least one balance element. With each balance element, an imbalance that otherwise exists is at least partially compensated, and improved concentricity is achieved. For this, the balance element is typically produced from a different material than the basic body, in particular a material with a greater density in comparison to the material of the basic body.